The major purposes of this research project are: 1) To study the formation of osteoclasts from precursors and determine the fate and turnover of nuclei in osteoclasts during the remodeling sequence. 2) Characterize the cellular and extracellular events taking p lace during the reversal phase and the formation of cement lines, morphological landmarks of the coupling between resorption and formation in the remodeling sequence. 3) Further evaluate the effects of diphosphonates, PTH, CT, and cortisol on the bone cells, the remodeling sequence and the bone balance.